1. Field of the Invention
The invention relates to printing machines, and more particularly to a method and an apparatus for fitting a printing plate, especially an offset printing plate, to an overhung plate cylinder of a rotary printing machine.
2. Description of the Related Art
DE 43 15 909 A1 shows a printing unit in which the plate cylinders are fitted with printing-plate sleeves. During printing operation, the plate cylinders are mounted on both sides in side walls. In order to change the printing-plate, supporting elements are removed from one side wall, after which the plate cylinders are overhung in the other side wall. The plate sleeves can than be drawn off the plate cylinders at the exposed sides of the latter and changed.
Plate sleeves advantageously consist of stainless steel, nickel or a nickel alloy, for example Hastelloy, and are well suited for erasable image-setting. In addition, these materials have good strength values. Plate sleeves of this type are clamped onto the plate cylinder by means of a press fit. In order to displace the plate sleeves for the purpose of changing them, they are usually expanded by means of compressed air.
Non-erasable printing plates advantageously consist of aluminium, and it is known to produce plate sleeves of this type from a butt-welded metal sheet. An apparatus which carries out a shaping and a joining step is needed for this. Such an apparatus is complicated and expensive, thus, production of plate sleeves of this type is correspondingly expensive.
EP-0 812 686 A2 shows an apparatus with which flat printing plates can be fitted axially to an overhung plate cylinder. For this purpose, the printing plates are pushed into a tube and, together with the tube, are pushed onto the plate cylinder over a mandrel, which expands the printing plate. As a result of the actuation of a plate clamping device, the printing plate is then clamped on the plate cylinder and the tube is removed from the plate cylinder. The disadvantage in this case is that the tube rests on the pre-imaged surface of the printing plate and, as a result, can cause damage to the printing surface.
DE 44 04 758 C2 refers to circularly bending a flat printing plate by hand, holding its legs together with an adhesive and subsequently pushing the printing plate axially onto a plate cylinder. The pushed on printing plate is then clamped by means of a clamping system.
The invention is based on the object of fitting overhung plate cylinders of a rotary printing machine cost-effectively with printing plates. Another object, is to enable flat printing plates to be clamped cost-effectively and reliably.
This and other objects are achieved in accordance with an embodiment of the invention, wherein flat printing plates can be cost-effectively imparted a sleeve shape, and enables these sleeves to be clamped by being axially pushed onto the plate cylinder. The production of these printing plates is compatible with development systems for printing plates which are common nowadays and can be found on the market. In various embodiments of the invention, there is also the possibility of clamping these printing plates using clamping systems for sleeves. The possibility is opened up of clamping sleeves and flat printing plates formed into sleeves, as desired, on a plate cylinder and, in addition, of choosing between erasable and non-erasable printing plates. The ability of the printing machine to be varied is therefore increased with a low outlay on costs. In addition, changing the printing plate axially by pushing it with the web threaded, reduces lost time. It is also possible for printing machines up to specific web widths to be designed in a space-saving manner without operating space between the printing units.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.